Implantable medical electronics devices consist of an implanted pulse generator that is used to provide electrical stimulation to certain tissues and an implantable lead or leads that are used to transmit the electrical impulse to the targeted tissues. Examples include cardiac pacemaking, and a number of related applications for cardiac rhythm management, treatments for congestive heart failure, and implanted defibrillators. Other applications for implantable pulse generators include neurostimulation with a wide range of uses such as pain control, nervous tremor mitigation, incontinent treatment, epilepsy seizure reduction, vagus nerve stimulation for clinical depression, and the like. This rapidly growing field will undoubtedly have even wider application in the future.
These implantable medical devices generally include an implanted pulse generator that generates electrical pulses or signals that are transmitted to a targeted tissue or tissues through an electrode on an implanted lead. Once the leads are implanted in the body, removal may involve major surgery with attendant risk factors. Therefore, a reliable method of connecting and disconnecting the leads from the implantable pulse generator is required in order to service or replace the implanted pulse generator.
Pulse generators are typically hermetically sealed housing containing circuitry and a power supply. Current practice is to place a molded header containing a connector on the housing to provide a structure to electrically couple with contact rings on the lead with the circuitry, such as illustrated in U.S. Pat. Publication No. 2003/0163171 (Kast et al.). While some pulse generators only require a few leads, pulse generators for some applications are very complex and require a large number of discrete electrical impulses each delivered by a discrete lead. In these more complex applications, each electrical impulse requires a discrete conductive path between the impulse generator and the lead electrode.
The proximal ends of the leads generally includes a series of conductive rings separated by insulating spacers so that when it is fully inserted into the connector assembly, each contact ring is placed in contact with a discrete contact. Each contact in turn is electrically coupled to a discrete lead on the circuitry for the implantable pulse generator.
The proximal ends of the leads serve as a male portion adapted to be received within a corresponding female connector on the implantable pulse generator housing. One such female electrical connector includes a cylindrical outer housing having a transverse circumferential groove or channel within the interior face of the housing. A metallic coil spring is disposed within the circumferential channel, providing electrical continuity between the spring and the outer metallic housing. Electrical connectors of this type are available from Bal Seal Engineering Company, Inc., Foothill, Calif., USA.
The male end bearing the conductive rings is preferably dimensioned to be insertable into the female portion with minimum force. The springs in the individual contacts provide a radially inward directed force on the contact rings to establish the electrical contact.
U.S. Pat. No. 4,655,462 (Balsells) discloses a coiled spring with a plurality of coils disposed in a preselected acute angle (i.e., pre-canted) with the centerline of the coil spring. The coil spring exerts a constant force in a loading direction approximately normal to the centerline of the coiled spring in response to a deflection of the coil spring along the loading direction. Pre-canted refers to each coil having a back portion disposed at a back angle with respect to the centerline and the forward portion disposed at a front angle with respect to the centerline, where the front angle being greater than the back angle before the coil spring is formed in a toroidal-shape.
U.S. Pat. Nos. 7,316,593 (Balsells) and 7,195,523 (Naviaux) disclose a connector assembly that uses a pre-canted spring to provide a fairly linear force-deflection curve during insertion of the contact end of the lead. The pre-canted spring also compensates for any irregularities on the surface of the contact rings on the lead. The pre-canted springs are typically retained in grooved housing or an annular ring that limits radial expansion, requiring very tight tolerances between the contact rings on the lead and the springs.
U.S. Pat. No. 7,110,827 (Sage) is directed to an electrical connector for medical leads having a solderless wiring connection to the circuitry in the implantable pulse generator. The housing includes at least one hole adjacent a mechanically deformable side wall for mechanically securing an electrical conductor inserted within the hole.
U.S. Pat. No. 7,299,095 (Barlow et al.) is directed to an electrical contact assembly including an annular housing defining an interior space. The housing includes a tubular wall having an outer surface facing the interior space, and an inner surface defining a central opening adapted to receive an electrical contact. Contained within the interior space of the housing is a garter spring encircling the outer surface of the wall under preload so that a portion of the inner diameter of the spring projects through the aperture into the central opening of the housing for engaging an electrical contact received within the central opening.